When I contacted the manufacturer of the Seacock valves on my boat
about this topic, Apollo Conbraco instructed me to NOT use a grease Zerk on the drain plug and to NOT force grease into that fitting because of the risk that high pressure grease injected will damage the soft PTFE spherical seal.
Assuming the objective is for ensuring the valve will have acceptable action during opening and closing, my solution was to remove the handle, remove the stem nut w/ the two nylon washer seals
, all while on the hard. Those parts
were all carefully cleaned, lubricated w/ marine
grease, then reassembled. The nut was tightened enough to prevent water intrusion, but not so tight that rotation was restricted.
It is possible to tighten that nut so much that rotation is impossible or difficult.
My seacock lever motion changed from very difficult to easy, with the action of flipping a light switch from this service
and has remained in this condition for over a decade. Prior to this service
zero improvement was attained by lubrication and by periodic seacock actuation.